1. Field of the Invention
This invention relates to ribbon feed means in typewriters and impact printers and more particularly to means for metering the ribbon being fed.
2. Description of the Prior Art
In conventional impact printers and typewriters, as the printing proceeds, the inventory of ribbon is moved from a portion on a supply spool to a take-up spool which winds up the ribbon after it is printed upon. In order to obtain a uniform ribbon feed, it has been traditional to provide means for metering the ribbon which is separate from the means for driving the take-up reel which winds the used ribbon. Such conventional ribbon metering means are extensively shown in the prior art. For example, U.S. Pat. No. 3,348,650, J. Meinherz et al, filed July 3, 1962 discloses such a ribbon metering apparatus wherein ribbon from a supply reel is metered so as to move at a uniform rate to a take-up reel (not shown). In such an apparatus, it would be conventional to have a separate drive mechanism for the take-up reel.
while such ribbon metering apparatus served the impact printer and typewriter technology very well for several generations and still continues to be significant, we have found that there is a potential for problems in this conventional approach. With the direction in the typewriter and printer art towards thinner and more fragile ribbons, tolerances within which these ribbons can withstand damage become much more limited. Consequently, where separate metering elements are used in printers, there appears to be an increasing possibility that the coordination of the operation of ribbon metering with the standard ribbon take-up drive may cause problems with respect to ribbon movement and stresses on the ribbon beyond the limited tolerances of such fragile ribbons.
Consequently, there is a need in the riboon feed technology for apparatus which eliminates separate ribbon metering and integrates the ribbon metering function into the ribbon take-up drive mechanism. Such apparatus will, in addition to minimizing the effects of ribbon feed which could damage fragile ribbons, also substantially reduce ribbon feed cost by eliminating such separate ribbon metering apparatus.
U.S. Pat. No. 3,923,141, Hengelhaupt, filed July 1, 1974, represents an approach taken in the art to eliminate separate ribbon metering drives. In the apparatus of this patent, the ribbon metering function is integrated with the ribbon take-up roller. The ribbon is metered at a uniform or constant rate by mechanical means which sense the radius of the ribbon portion on the take-up spool, and through a series of rather complex mechanical linkages constantly vary the velocity of the peripheral take-up reel drive roller with changes in radius of the ribbon portion on the take-up reel so that the ribbon moves at a uniform rate. While such apparatus does eliminate separate ribbon metering mechanism, its complex mechanical linkages would appear to have a greater possibility for ribbon metering and drive irregularities which could potentially damage the relatively fragile ribbons currently in extensive usage.